staggered drives v std drives
 

Tech help , given similar engines, 2 X(722) s/chargd, huber 1450s, drives (6`s wet sump )and props 5 blade cleaver 32 pitch. what performance % increase would be found by re positioning engines from present std side by side set up to staggered set up.
Old Cigarette undergoing major refit so serious work involved not a problem. understand staggered advantages from weight and C og G distribution , ease of working on engines etc but how does the relationship and distance apart of each prop in the water achieve maximum thrust, are their any technical papers orstuff that u know of or is it simply copying existing staggered set ups?
Boat originally appears to have once had a staggered set up in a previous life. So is it worth doing?

while i have tons of data to support answers to your questions....the easy answer is staggering them will make your life so much easier to work on them!!!

but what parts do u have? some forget to factor in the large expense of staggered exhaust systems.

cheers mate

Good point. their on Stellings, so would need two extension
pieces.
what I was really getting at, if all the main existing components were used, what across the water speed difference the staggered set up would give.
if Im pulling say 95 side by side would a staggered give 98 or what increase would be expected, if any, say in a typical Cig staggered layout?

Thanks,

nothing worth doing with todays prop technology for a performance gains on a pleasure boat. moving 1500 lbs forward in a designed pleasure boat can be detrimental. raising the drives further out of the water, changing gear ratios, and working something out with herring for prop swapping would the best thing to do for performance. if money was not an issue than i would do it from; i can't stand working on side by side engines! but then again some staggered engines are shoehorned in there too!

cheers

What hull are you doing it in? full cabin, half cabin, no cabin?

Biggest benefit is rough water handling. The roll inertia is much less since the rolling mass is closer to the centerline of the direction of travel. Motors are usually also able to be mounted lower in the hull for a given x-dimension.

Getting too much weight forward can be a drawback, too, so you have to get your batteries and fuel moved aft.

In smooth water, at sub-100mph speeds, I don't know that there would be enough speed difference to measure (assuming x-dims remain the same in relation to the height at the drive centerline).

MC

"The roll inertia is much less since the rolling mass is closer to the centerline of the direction of travel."

a misconception perpetuated by manufacturers that this is a good thing. waves have a far greater forces than those the boat can generate...totally unlike a car or airplane...loosing the moment of inertia in a boat can be a huge disadvantage.

Audacity, so are you saying by moving the engines (weight)twards center is not really helping.

in any application i love working on staggered engine set ups. the cost of adding very custom exhaust systems for a staggered set up can be....staggering tho.

for racing it's easier to balance the boat length wise. but it places the drives in place where the flow is much more consistent. being able to move weight around where you want it to met minimum weight requirements is always a bonus.

think of it this way: if you are holding 100 pounds and your goal is to manipulate (accelerate) it then you would want to be holding a dumbbell. if your goal is to resist an outside force to accelerate it? say someone giving it a bump. then you would want to be holding onto a barbell. your holding both at the CG but both have very different moments of inertia.

I wish there was a easy answer to this question backed with testing and proof. No disrespect to any answers on here, they all have helped my brain spin, but now I am thinking to much and its driving me crazy!!!

How did the 35 fountain go from like 85 to 101 overnight? I thought a large part was due to staggering the engines? Obviously higher X, props, etc. could contribute. Still there are not many 525 boats 32-35 running 101mph!!! (btw I am not a fountain fan)

Maybe Coolerman can chime in, they did an amazing job changing thier black thunder to staggered. They won at LOTO and currently run about 129mph! Full cabin 9'6" wide floating condo! Impressive. Stand up guys also.

i have rigged and de-rigged a donzi 38 zr F2 boat many times. same with a donzi 38 zr super v...all the same hull....standard, staggered. different centers. more x dimensions than one would believe. standard transom assemblies, ITS, and stand off boxes.
i kinda have an idea what works.

now for the speed gains....prop technology. once people got over slip numbers...running 1.32 vs 1.5 with very high x dim, ITS boxes, and 6 blades was prob worth 10 mph!

when i say de rigged....i mean pulling EVERYTHING off the transom and plugging it and starting over!

ps high x dimensions and prop technology also led to using number 6 dives in a 525 application...10 years prior it would have probably knocked off 20 mph!

most speeds people talk about are all BS!

and if you think for one second i would send a boat to a boat mag test with stock 525's!....more like 600+! or stock out of the mold hull?! props out of the merc box....i think not.

thanks for your input.
Offshoredrillin. ; Hull is a stripped out Cigarette 35 flatdeck,
tony toll`s old classic UK offshore boat "Adnania".

Mcollinstn/Audacity : getting the weight as low as possible and as near to the centre line as possible , from point of the
moment of inertia and C of G makes total sense. I guess the difficult part is trimming the boat (bow attitude) for moving
1500 lbs 3 feet or so, furthur forward. moving other weight etc.

If the kind of improvement mentioned on this thread,
35 fountain +26mph and the black boat 125mph then that really makes it worthwhile.
The engines have reserves of power wot 1200hp each at 5600 its just applying it in the best way to the water to give ideal performance.

I was interested in the thrust produced by like components and power in the two alternative
prop positions side by side / staggered.
I would have thought that staggered props, may by virtue of being in close proximity, work more efficiently to produce one larger combined thrust stream?
whereas side by side would be more independent thrusts.producing slightly less effect.
I may be thinking crap, props are 5 blade cleaver 17.5 x 36

forgot to advise prop position and ratio.
1:36 No6 Wets. Current prop center line , 31/2" directly below hull on each drive now Side by side.
Difficult to get prop center line level with hull boat without
raising engines and C of G.
thanks for all the numbers.

I have always wondered about this same question.

When i look at most raceboats with staggered configurations usually they saddle tanks along with possibly floor tanks for fuel. Is this to have a more stable relation of weight as it affects CG and as Audacity mentions moment of inertia as it the fuel is consumed?

I would think in a side by side situation with floor tanks as the fuel is consumed the CG is moving backwards towards the stern changing the CG. It seams this could be trouble in a stepped botom boat as it will ride differently as that CG changes.

With the saddle tanks a good portion of the fuel is in the area around the engines which as it is used is would be less of a change to the CG.

As far as weight being mounted lower in the hull -- i would think the saddle tanks would negate any effect of the engines being mounted lower. Due to the fact that the fuel would be located below the floor in a side by side...

I'm all ears on this as i look at a bare hull needing to b rigged....

Dave

a 35 foot boat with 2400 hp is too small of a hull for it...all that money in rigging....why not start with a more efficient better handling hull with stock power?

anything with over 750hp should b staggered....u will spend more time working on them than boating. it will make it easier to work on! it's about that easy.

does the boat have belly gas tank under the cockpit floor?

yes belly tanks. currently 2 x 125 gallons located approx under and forward of drivers/navigators feet. (cig 35 flatdeck).each side of center line.

video on U tube "mission impossible cigarette isle of wight" from memory, shows it used to run pretty well.
side by side, a few years ago, with 540`s then.

original engine 722 test on U tube "Merlin supercharged marine big block"
Weve got the parts weve got so its making the best out of them.

Lots of work to remove the cockpit floor, remove belly tanks, move bulkhead at the rear of the tanks forward, then shorten cockpit and build new stringer system. Then you have to build new hatches, repair the deck and put in a new transom.

I'm one for doing projects but that is getting to be a big one.